WeeChat (Wee Enhanced Environment for Chat) is a fast and light IRC client for many operating systems. Everything can be done with a keyboard, and it is customizable and extensible with C plugins and scripts. It is compliant with RFCs 1459, 2810, 2811, 2812, and 2813.

MCabber is a small Jabber console client. It features SASL/TLS/SSL support, multi-user chat, PGP support, history logging, dynamic modules, and external actions triggers. It also has support for Aspell/Enchant for spell checking and OTR (Off-The-Record) messaging.

GOZERBOT is a channel bot that aids conversation in IRC channels and Jabber conference rooms. It's mainly used to serve RSS feeds and to have custom commands made for the channel. More then just a channel bot, GOZERBOT aims to provide a platform for the user to program his own bot and make it
into something useful. This is done with a plugin structure that makes it easy to program your own. There are over 100 plugins already written and ready for use.

Prosody is a server for Jabber/XMPP written in
Lua. It aims to be easy to use and light on
resources. For developers, it aims to give a
flexible system on which to rapidly develop added
functionality or prototype new protocols.

xmppony is an XMPP library for Python. It's a fork of xmpppy, which was in turn a fork of jabber.py. It is currently a drop-in replacement for python-xmpp (xmpppy), with some bugs fixed and file transfer added.

Saros is a Eclipse plugin for collaborative text editing that in particular targets distributed pair programming (also called remote pair programming), but can support arbitrarily many participants at once. All members of a session have an identical copy of an Eclipse project and Saros keeps these copies in sync as editing progresses.